This invention relates generally to single or multi-pole circuit breakers, and more particularly to circuit breakers having improved movable contact structures.
The basic functions of circuit breakers are to provide electrical system protection and coordination whenever abnormalities occur on any part of the system. The operating voltage, continuous current, frequency, short circuit interrupting capability, and time-current coordination needed are some of the factors which must be considered when designing a breaker. Government and industry are placing increasing demands upon the electrical industry for interrupters with improved performance in a smaller package and with numerous new and novel features.
Stored energy mechanisms for use in circuit breakers of the single pole or multi-pole type have been known in the art. A particular construction of such mechanisms is primarily dependent upon the parameters such as rating of the breaker. Needless to say, many stored energy circuit breakers having closing springs cannot be charged while the circuit breaker is in operation. For that reason, some circuit breakers have the disadvantage of not always being ready to close in a moment's notice. These circuit breakers do not have, for example, an open-close-open feature which users of the equipment find desirable.
Another problem present in some prior art circuit breakers is that associated with matching the spring torque curve to the breaker loading. These prior art breakers utilize charging and discharging strokes which are each 180.degree.. The resulting spring torque curve is predetermined, and usually cannot be matched with the breaker loading. Such a predetermined curve mandates that the elements associated with the breaker be matched for this peak torque rather than be matched with the breaker load curve.
An additional problem present in the prior art circuit breakers is associated with the means for connecting the movable contact to one of the stationary contacts. These prior art connections generally included the use of braids or laminations which were secured to both the movable contact and one of the stationary contacts, and more particularly, the load side stationary contact. These braids are not always desirable, in that they may include some slack which could interfere with normal breaker operations.
Still another problem present in prior art circuit breakers is associated with the contact pressure between the movable and stationary contacts. These contacts are subject to high forces when carrying high fault currents, which forces tend to separate the contacts apart. In many cases, however, the contacts are required to stay closed for a period of time when conducting the high currents for coordination purposes. This is referred to as the withstand or short time rating of a breaker. One method utilized to keep contacts closed during this period uses high spring forces to force the movable contact against the stationary contact. This use of spring forces is unsatisfactory, as it increases the costs of the breaker, the complexity of the operating mechanism, and requires a higher force to reset the breaker. Another method utilizes movable current carrying conductors at the stationary conductor, and these movable current carrying conductors are positioned with respect to connecting conductors so as to have a magnetic repulsion force assisting the contact force. This method, however, requires additional space in the breaker and also requires the use of an extra length of current carrying conductors.